PicoKeys v2

Rust-based security key firmware supporting FIDO2/CTAP2, OATH-TOTP/HOTP, and HSM functionality across multiple embedded platforms.

Supported Platforms

Platform	MCU	USB	Transport	Notes
RP2040	ARM Cortex-M0+ (dual core, 133 MHz)	USB 1.1 FS	HID + CCID	No OTP fuses, MKEK in flash
RP2350	ARM Cortex-M33 / RISC-V (dual core, 150 MHz)	USB 1.1 FS	HID + CCID	OTP fuses, ARM TrustZone, dedicated TRNG
ESP32-S3	Xtensa LX7 (dual core, 240 MHz)	USB OTG FS	HID + CCID	eFuse MKEK, Secure Boot V2, HW bignum accelerator
ESP32-C5	RISC-V (single core)	USB OTG FS	HID + CCID	eFuse MKEK, Secure Boot V2
ESP32-C6	RISC-V (single core, 160 MHz)	USB-Serial-JTAG	Serial bridge only	⚠️ No native HID/CCID — CLI-only mode via serial
SAMD21	ARM Cortex-M0+ (48 MHz)	USB FS	HID + CCID	256 KB flash limit, no RSA, no HSM

Feature Matrix

Feature	RP2040	RP2350	ESP32-S3	ESP32-C5	ESP32-C6	SAMD21
FIDO2/CTAP2	✅	✅	✅	✅	✅¹	✅
U2F/CTAP1	✅	✅	✅	✅	✅¹	✅
OATH TOTP/HOTP	✅	✅	✅	✅	✅¹	✅
HSM (SmartCard-HSM)	✅	✅	✅	✅	✅¹	❌²
RSA-2048/4096	✅	✅	✅	✅	✅¹	❌²
ECC (P-256, P-384, Ed25519)	✅	✅	✅	✅	✅¹	✅
Secure Boot	❌	✅	✅	✅	✅	❌
Hardware TRNG	❌³	✅	✅	✅	✅	❌³
Press-to-Confirm	✅	✅	✅	✅	✅	✅⁴

¹ ESP32-C6: Serial bridge only — not usable as native FIDO2 authenticator in browsers; requires picokeys-cli host-side serial transport.
² SAMD21: 256 KB flash constraint excludes RSA and HSM application.
³ RP2040 uses ROSC-based entropy (weak); SAMD21 has limited TRNG.
⁴ SAMD21: No BOOTSEL button; configurable GPIO, default simulated always-confirmed.

Quick Start

Prerequisites

# Install Rust nightly toolchain (see rust-toolchain.toml)
rustup show

# Install target for your platform
rustup target add thumbv6m-none-eabi          # RP2040, SAMD21
rustup target add thumbv8m.main-none-eabihf   # RP2350
rustup target add riscv32imac-unknown-none-elf # ESP32-C5, ESP32-C6

# For ESP32-S3 (Xtensa)
cargo install espup
espup install

Build

# RP2040
cargo build --release -p pico-rs-fido --features rp2040

# RP2350
cargo build --release -p pico-rs-fido --features rp2350

# ESP32-S3
cargo build --release -p pico-rs-fido --features esp32s3

# ESP32-C5
cargo build --release -p pico-rs-fido --features esp32c5

# ESP32-C6 (serial bridge mode only)
cargo build --release -p pico-rs-fido --features esp32c6

# SAMD21 (FIDO2 + OATH only, no RSA/HSM)
cargo build --release -p pico-rs-fido --features samd21

# HSM application (not available on SAMD21)
cargo build --release -p pico-rs-hsm --features rp2350

CLI Installation

cargo install --path picokeys-cli
picokeys-cli info

Fuzz Testing

cargo install cargo-fuzz
cd fuzz
cargo fuzz run fuzz_ctap_cbor
cargo fuzz run fuzz_ccid_apdu
cargo fuzz run fuzz_credential_decode
cargo fuzz run fuzz_hid_framing

Architecture

┌──────────────────────────────────────────────────────┐
│                   picokeys-cli                       │
│           (Host CLI — USB HID / CCID / Serial)       │
└──────────────┬───────────────────────┬───────────────┘
               │ USB HID              │ USB CCID
┌──────────────▼───────────┐ ┌────────▼───────────────┐
│      pico-rs-fido        │ │      pico-rs-hsm       │
│  ┌─────────────────────┐ │ │  ┌──────────────────┐  │
│  │ CTAP2 Command Router│ │ │  │ APDU Dispatcher  │  │
│  ├─────────────────────┤ │ │  ├──────────────────┤  │
│  │ MakeCredential      │ │ │  │ Key Management   │  │
│  │ GetAssertion        │ │ │  │ Crypto Ops       │  │
│  │ ClientPIN v1/v2     │ │ │  │ DKEK / Shamir    │  │
│  │ CredentialMgmt      │ │ │  │ Certificate Mgmt │  │
│  │ OATH TOTP/HOTP      │ │ │  │ Secure Messaging │  │
│  │ U2F Compat          │ │ │  │ PIN Management   │  │
│  └─────────────────────┘ │ │  └──────────────────┘  │
└──────────────┬───────────┘ └────────┬───────────────┘
               │                      │
┌──────────────▼──────────────────────▼───────────────┐
│                    pico-rs-sdk                       │
│  ┌──────────┐ ┌────────┐ ┌───────┐ ┌─────────────┐ │
│  │ Transport│ │ Crypto │ │Storage│ │ LED / Button│ │
│  │ HID+CCID │ │ AES,ECC│ │ Flash │ │ User Pres.  │ │
│  └────┬─────┘ │ RSA,Ed │ └───┬───┘ └──────┬──────┘ │
│       │       └────────┘     │             │        │
│  ┌────▼──────────────────────▼─────────────▼──────┐ │
│  │            Platform Adapters                    │ │
│  │  RP2040 │ RP2350 │ ESP32-S3 │ C5 │ C6 │ SAMD21│ │
│  └─────────────────────────────────────────────────┘ │
└──────────────────────────────────────────────────────┘

Security

See SECURITY.md for the full security policy, including:

• Key material protection (zeroize + ZeroizeOnDrop)
• Constant-time comparisons (subtle::ConstantTimeEq)
• Credential encryption (AES-256-GCM)
• PIN storage (PBKDF2-HMAC-SHA256, 256k iterations)
• Known advisory: RUSTSEC-2023-0071 (RSA Marvin Attack)
• Secure boot provisioning for RP2350 and ESP32
• Platform-specific security comparison

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contributing

Contributions are welcome! Please:

1. Fork the repository and create a feature branch
2. Ensure cargo build and cargo test pass for your target platform
3. Run cargo clippy with no warnings
4. Follow the existing code style — zeroize on all key material, subtle for secret comparisons
5. Open a Pull Request with a clear description of changes

For security-sensitive contributions, please review SECURITY.md before submitting.